When it comes to Kniphofia propagation, by far the easiest method is division in the Autumn or Spring. To do this, pick an established plant with a well developed crown. Select a region of the crown from which one to several distinct rosettes are present – preferably slightly away from the rest of the rosettes. Using either a sharp spade or knife, cut entirely through the crown to divide off the new section then carefully dig up that crown area (preferably with a good root system), leaving the rest of the plant intact in the ground.
You can then either further divide this crown section to make several plants or pot it on as is – either way pot plants on into a somewhat gritty compost mix, ensuring the crown is proud of the soil in the pot. Keep the pot well watered and within a month or two the plant should have developed a healthy root system and be ready for planting out. If preferred divisions can also be immediately planted out into the garden, again taking care to plant with the crown slightly proud.
Kniphofia also grow very well from seed – assuming of course that you do not expect them to be the same as the parent plant. Kniphofia are fairly promiscuous so the resulting seedlings are likely to be an array of crosses. By moving pollen from the stamens of one plant to the stigma of another you can try and control the crosses but far easier is to simply allow the bees to cross pollinate the plants for you and enjoy the unpredictable results!
Kniphofia seeds should be collected only once the seed pods have entirely dried (turning a brown colour) and begun opening such that the seeds are easily liberated if the flower stem is shaken. Kniphofia seeds are a fairly easy to handle being a standard size, vaguely triangular in shape and dark black in colour.
I find the best germination success comes when Kniphofia seeds are sown in the Autumn into a standard seed compost, topped with grit, kept well watered and left outside over winter. Fresh seeds may well germinate in the Autumn however exposure to cold over the winter tends to help break any lingering dormancy – and if such over-wintered seeds are brought into a greenhouse in Spring they should germinate rapidly.
Kniphofia seedlings should then be left in the seed tray until they have developed a few strong leaves after which they can be potted on individually – again ensuring they are not planted too deeply! You can expect your first flowers within a couple of years from seed sowing.